Quantitative analysis method of charge state of layered lithium battery positive electrode material

Abstract

The application discloses a quantitative analysis method of a charged state of a layered lithium battery positive electrode material, determines a standard curve between a relative peak intensity value of a characteristic peak and the charged state of the layered positive electrode material through in-situ / non-in-situ Raman spectrum testing in a first constant current charging / discharging process, estimates the charged state of a to-be-tested sample through the relative peak intensity value of the Raman spectrum characteristic peak and other data, and quantitatively analyzes the uniformity of the charged state distribution of multiple space scales such as an electrode surface / cross section and a material particle surface / interior in combination with a Raman spectrum imaging technology and an ion beam cutting technology. The application mainly solves technical problems such as a complicated calculation process, an influence of external factors, a single space scale and special devices and equipment in a previous positive electrode material charged state estimation method in a lithium ion battery failure analysis process, and provides a device and a method for conveniently and quickly, multi-space-scale and quantitatively analyzing the charged state of the lithium battery positive electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical spectroscopy, in particular to a quantitative analysis method of the charge state of a layered lithium battery cathode material. BACKGROUND

[0002] The cathode material is one of the decisive factors of the performance of lithium ion batteries, and the layered cathode material, such as LiNi x Co y Mn z O2(x+y+z=1,0≤x,y,z≤1)、LiNi x Co y Mn z Al n O2(x+y+z+n=1,0.8≤x≤1,0≤y≤0.2,0≤z≤0.2,0<n≤0.2)、aLi2MnO3·(1-a)LiNi x Co y Mn z O2(x+y+z=1,0<a<1,0.5≤x≤1,0≤y≤0.5,0≤z≤0.5) and the like have become one of the mainstream cathode materials of the current power lithium ion batteries. However, in the actual use process, the layered cathode material still faces many problems leading to the deterioration of its electrochemical performance and safety performance. The estimation of the charge state is one of the key links of the failure analysis of lithium ion batteries. Accurate analysis of the size and spatial distribution of the charge state of the layered cathode material can reflect the real utilization rate of the cathode material and the reaction uniformity inside the electrode, which is an important parameter for analyzing the root cause of battery failure, guiding the modification of the cathode material, optimizing the electrode structure design, and improving the battery performance.

[0003] The commonly used methods for detecting the charge state of lithium ion batteries at present include open circuit voltage method, ampere-hour integration method, internal resistance method, pressure detection method and the like. However, such methods have the following disadvantages: (1) the average charge state of a large number of cathode particles on the scale of the battery or electrode is obtained, which cannot be used to analyze the charge state difference of multiple spatial scales such as the electrode surface / cross section, the cathode particle surface / interior and the like; (2) a complex calculation process is usually needed to establish the corresponding relationship between the measured parameters and the charge state; (3) the estimation result is easily affected by other battery components, temperature, self-discharge and the like. The characterization technology based on structural characteristics can not be affected by external factors, and can study the intrinsic charge state of the cathode material from multiple spatial scales, and the most commonly used characterization technology is X-ray absorption spectroscopy and its derivative technology. However, X-ray absorption spectroscopy usually needs the support of special synchrotron radiation sources, and is difficult to conveniently and quantitatively estimate the charge state of the cathode material. SUMMARY

[0004] In view of this, the present application mainly solves the technical problems of the original positive material charge state estimation method in the lithium ion battery failure analysis process, such as complicated calculation process, easy to be affected by external factors, single spatial scale, special device equipment, etc., and provides a device and method for quantitative analysis of lithium battery positive material charge state which is convenient and fast, multi-spatial scale and quantitative analysis. The technical solutions of the present application are as follows:

[0005] A quantitative analysis method of layered lithium battery positive material charge state, the method comprises the following steps:

[0006] (1) A standard electrode is prepared with fresh layered positive material, conductive agent, binder and stainless steel mesh, and a center opening conductive upper cover, standard electrode, separator, electrolyte, lithium sheet and conductive base are assembled into a button cell assembly, which is loaded into an in-situ Raman spectrum pool. The in-situ Raman spectrum pool comprises an upper cover made of conductive material and a base made of insulating material, which are overlapped and tightly connected together through a sealing ring and a screw bolt; the central part of the conductive upper cover is provided with an opening, and the bottom of the opening is provided with a window piece made of transparent material; the central part of the upper end surface of the insulating base is provided with a battery assembly groove, and a conductive spring is arranged below the battery assembly groove; a conductive screw is arranged on the side wall of the insulating base, one end of the conductive screw extends from the base, the other end of the conductive screw is in contact with the conductive spring in the base, and a sealing ring is arranged at the contact position between the conductive screw and the side wall of the base; the conductive screw, the conductive spring, the battery assembly and the conductive upper cover form a conductive path;

[0007] The in-situ Raman spectrum pool used in the present application has a simple assembly process, all components (except the separator and lithium sheet) can be disassembled and cleaned for repeated use, does not require special light source, and has simple operation, excellent sealing performance, excellent electrochemical performance and excellent spectral performance;

[0008] (2) The standard curve between the relative peak intensity value of the Raman spectrum characteristic peak and the material charge state is determined through in-situ electrochemical Raman spectrum test in the first cycle of constant current charge / discharge process;

[0009] The test conditions of the in-situ electrochemical Raman spectrum are as follows: the laser wavelength is 532-786nm, the laser power is 0.03-0.30mW, the single spectrum acquisition time is 100-900s, the rate of constant current charge / discharge test is 0.1-0.2C, the small rate ensures the uniformity of the internal electrochemical reaction of the electrode, and the voltage interval is 2.8-4.8V; the calculation method of the material charge state is as follows: charge state=(theoretical specific capacity-charge specific capacity+discharge specific capacity) / theoretical specific capacity*100%;

[0010] (3) under the same laser wavelength and power conditions, Raman spectrum test is performed on the layered cathode material / electrode sample to be analyzed, the relative peak intensity value of the measured Raman spectrum characteristic peak is calculated, and the charged state of the sample to be analyzed is estimated according to the standard curve in step (2);

[0011] The spatial resolution of the Raman spectrum test is about 1 μm, and the particle size of the layered cathode material is usually 3-20 μm, so the charged state distribution of the material particle surface or the electrode surface can be analyzed by the Raman spectrum imaging test, or the cross section of the particle / electrode to be measured is prepared by the ion beam cutting technology, and then the charged state distribution of the cross section of the particle / electrode is analyzed by the Raman spectrum imaging test, so that the multi-space scale quantitative analysis of the charged state of the lithium battery layered cathode material is realized.

[0012] The present application has the following advantages:

[0013] The in-situ Raman spectrum cell used in the present application has a simple assembly process, all components (except the diaphragm and lithium sheet) can be disassembled and cleaned for repeated use, does not require a special light source, is easy to operate, has excellent sealing performance, electrochemical performance and spectral performance, and the distance between the battery assembly and the window sheet can be adjusted by the conductive spring to match battery assemblies of different thicknesses.

[0014] The standard curve between the relative peak intensity value of the characteristic peak and the charged state of the layered cathode material (which is a one-to-one relationship) is determined by the in-situ / non-in-situ Raman spectrum test in the first constant current charge / discharge process; the standard curve of the same layered cathode material is unique, and does not need to be repeatedly tested, and can be used for failure analysis of multiple batches of lithium ion batteries; low power and long time spectrum acquisition can ensure the spectral signal-to-noise ratio and avoid laser heat effect damage to the sample;

[0015] The charged state of the sample to be measured is estimated by the relative peak intensity value of the Raman spectrum characteristic peak; there is no special sample preparation requirement, and the test operation is convenient and fast; the test result is reliable and is not affected by other factors such as battery components, temperature and self-discharge;

[0016] The Raman spectrum imaging technology and the ion beam cutting technology are combined to quantitatively analyze the charged state distribution uniformity of multiple space scales such as the electrode surface / cross section and the material particle surface / interior; the sample pretreatment operation is simple, and the spatial distribution result of the charged state is self-evident.

[0017] Therefore, the present application mainly solves the technical problems of the original cathode material charged state estimation method in the lithium ion battery failure analysis process, such as complicated calculation process, easy to be affected by external factors, single spatial scale and special device equipment, and provides a device and method for conveniently and quickly, multi-space scale and quantitatively analyzing the charged state of the lithium battery cathode material. BRIEF DESCRIPTION OF DRAWINGS

[0018] Fig. 1 This is a schematic diagram of the assembly of the in-situ Raman spectroscopy cell in this invention;

[0019] Fig. 2 (a) is the in-situ Raman spectrum of the layered cathode material during the first charge-discharge cycle; (b) is the standard curve between the relative peak intensities of the Raman spectrum characteristic peaks and the material's charge state; it was found that the relative peak intensity ratio I[A] 1g (Ni)] / I[E g (Mn)] and I[E g (Ni)] / I[E g (Mn)] With Li + Increased with the expulsion of Li; + The re-embedded structure gradually restored the two ratios to a state close to the initial spectral ratio.

[0020] Fig. 3 This is a schematic diagram of multi-spatial-scale Raman imaging of layered cathode materials. Raman spectroscopy imaging tests are performed on the surface of a single cathode particle or the electrode surface of a rectangular region to achieve spatial-scale analysis of the charge state distribution on the particle surface or electrode surface. Alternatively, ion beam cutting technology can be used to obtain the electrode cross-section, and Raman spectroscopy imaging tests are performed on the cross-section of a single particle or the electrode cross-section of a rectangular region to achieve spatial-scale analysis of the charge state distribution on the particle cross-section or electrode cross-section.

[0021] In the diagram: 1. Conductive top cover; 2. Standard electrode; 3. Diaphragm; 4. Lithium sheet; 5. Conductive base; 6. Top cover; 7. Base; 8. Conductive spring; 9. Conductive screw. Detailed implementation method:

[0022] Combined with appendix Figs. 1-3 The present invention provides a further explanation of a quantitative analysis method for the charge state of a layered lithium-ion battery cathode material.

[0023] The present invention provides a quantitative analysis method for the charge state of layered lithium battery cathode materials, the method comprising the following steps:

[0024] S1, with fresh layered positive material, conductive agent, binder, stainless steel mesh to prepare standard electrode 2, and with center opening conductive upper cover 1, standard electrode 2, separator 3, electrolyte, lithium sheet 4, conductive base 5, etc. Assembled into a button cell assembly, put into an in-situ Raman spectroscopy cell, the in-situ Raman spectroscopy cell includes an upper cover 6 made of conductive material and a base 7 made of insulating material, both of which are overlapped and tightly connected together through a sealing ring 7 in the middle and a screw bolt; the central part of the upper cover 6 is provided with an opening, and the bottom of the opening is provided with a window sheet made of transparent material; the upper end surface of the base 7 is provided with a battery assembly groove, and the lower part of the battery assembly groove is provided with a conductive spring 8; a conductive screw 9 is arranged on the side wall of the base 7, one end of the conductive screw 9 extends from the base 7, and the other end is in contact with the conductive spring 8 in the base 7, and a sealing ring is arranged at the contact position of the conductive screw 9 and the side wall of the base 7; the conductive screw 9, the conductive spring 8, the battery assembly, and the upper cover 6 form a conductive path;

[0025] The in-situ Raman spectroscopy cell used in the patent has a simple assembly process, all components (except the separator 3 and the lithium sheet 4) can be disassembled and cleaned for repeated use; no special light source is needed, and the operation is simple; the sealing performance, electrochemical performance and spectral performance are excellent;

[0026] S2, through the in-situ electrochemical Raman spectrum test of the first cycle of constant current charge / discharge process, it is determined that the standard curve between the relative peak intensity value of the Raman spectrum characteristic peak and the material charge state is a one-to-one corresponding relationship, and the Fig. 2 (b) the relative peak intensity ratio I[A 1g (Ni)] / I[E g (Mn)] and I[E g (Ni)] / I[E g (Mn)] increases with the extraction of Li + ; with the re-embedding structure of Li + , the two ratios gradually return to the state close to the initial spectrum ratio;

[0027] Wherein, the test conditions of in-situ electrochemical Raman spectrum are: laser wavelength is 532-786nm, laser power is 0.03-0.30mW, single spectrum acquisition time is 100-900s, constant current charge / discharge test rate is 0.1-0.2C, small rate ensures the uniformity of internal electrochemical reaction, voltage interval is 2.8-4.8V; the calculation method of material charge state is: charge state=(theoretical specific capacity-charge specific capacity+discharge specific capacity) / theoretical specific capacity*100%;

[0028] S3, under the same laser wavelength and power conditions, the Raman spectrum of the layered positive electrode material / electrode sample to be analyzed is tested, the relative peak intensity value of the measured Raman spectrum characteristic peak is calculated, and the charge state of the sample to be analyzed is estimated according to the standard curve in S2,Fig. 3 The electrode surface of a single positive electrode particle surface or a rectangular area is selected for Raman spectrum imaging test, so as to realize the analysis of the charged state distribution of the particle surface or the electrode surface in the same spatial scale; the ion beam cutting technology can be used to obtain the cross section of the electrode, and the cross section of a single particle or the cross section of the electrode in a rectangular area is selected for Raman spectrum imaging test, so as to realize the analysis of the charged state distribution of the particle cross section or the electrode cross section in the same spatial scale;

[0029] In the formula, the spatial resolution of the Raman spectrum test is about 1 μm, and the particle size of the layered positive electrode material is usually 3-20 μm; the charged state distribution of the material particle surface or the electrode surface can be analyzed by the Raman spectrum imaging test, or the cross section of the particle / electrode to be tested is prepared by the ion beam cutting technology, and then the charged state distribution of the particle / electrode cross section is analyzed by the Raman spectrum imaging test, so as to realize the quantitative analysis of the charged state of the lithium battery layered positive electrode material in multiple spatial scales.

[0030] The above only describes the preferred embodiments of the present application, and all other embodiments obtained by those skilled in the art without creative labor shall belong to the protection scope of the present application.

Claims

1. A method for quantitative analysis of the charge state of a layered lithium battery cathode material, characterized by, Comprising the following steps: Step one, use fresh layered positive material, conductive agent, binder and stainless steel mesh to prepare standard electrode, layered positive material includes LiNi x Co y Mn z O2(x+y+z=1, 0≤x,y,z≤1), LiNi x Co y Mn z Al n O2(x+y+z+n=1, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2, 0<n≤0.2), aLi2MnO3·(1-a)LiNi x Co y Mn z O2(x+y+z=1, 0<a<1, 0.5≤x≤1, 0≤y≤0.5, 0≤z≤0.5) one, and then use the center opening conductive upper cover, standard electrode, separator, electrolyte, lithium sheet and conductive base to assemble into a button cell assembly, and then put into an in-situ Raman spectroscopy cell. Step two, through the in-situ electrochemical Raman spectrum test of the first cycle constant current charge and discharge process, the standard curve of the relative peak intensity ratio of the Raman spectrum characteristic peaks A1g (Ni) peak and Eg (Mn) peak and the material charge state is determined; Step three, under the same laser wavelength and power conditions, the Raman spectrum test is carried out on the layered positive electrode material sample to be analyzed, the relative peak intensity ratio of the measured A1g (Ni) peak and Eg (Mn) peak is calculated, and the charge state of the sample to be analyzed is estimated according to the standard curve in step two, and step three includes any one of the following analysis methods: (a) Through Raman spectrum imaging test analysis of the charge state distribution of the material particle surface or the electrode surface, the quantitative analysis of the lithium battery layered positive electrode material charge state is realized, the spatial resolution of the Raman spectrum test is 1 μm, and the particle size of the layered positive electrode material is 3-20 μm; (b) Through ion beam cutting technology to prepare the cross section of the particle / electrode to be measured, and then use Raman spectrum imaging test to analyze the charge state distribution of the particle / electrode cross section, realize the quantitative analysis of the lithium battery layered positive electrode material charge state, the spatial resolution of the Raman spectrum test is 1 μm, and the particle size of the layered positive electrode material is 3-20 μm.

2. The method for quantitative analysis of the charge state of a layered lithium battery cathode material according to claim 1, characterized in that: The in-situ Raman spectrum pool in step one includes an upper cover made of conductive material and a base made of insulating material, which are overlapped, a sealing ring is arranged in the middle, and they are tightly connected together through screws and bolts; The central part of the conductive upper cover is provided with an opening, and the bottom of the opening is provided with a window piece made of transparent material; The upper end surface of the base is provided with a battery assembly groove in the center, and a conductive spring is arranged below the battery groove; A conductive screw is arranged on the side wall of the base, one end of the conductive screw extends from the base, the other end contacts the conductive spring in the base, and a sealing ring is arranged at the contact position of the conductive screw and the side wall of the base; The conductive screw, the conductive spring, the battery assembly and the conductive upper cover form a conductive path.

3. The method for quantitative analysis of the charge state of a layered lithium battery cathode material according to claim 1, characterized in that: The test conditions of the in-situ electrochemical Raman spectrum in step two are that the laser wavelength is 532-786 nm, the laser power is 0.03-0.30 mW, the single spectrum acquisition time is 100-900 s, the constant current charge and discharge test rate is 0.1-0.2 C, and the voltage interval is 2.8-4.8 V; The calculation method of the material charge state is Charge state = (theoretical specific capacity-charging specific capacity+discharging specific capacity) / theoretical specific capacity * 100%.

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